NEW YORK (AFP) - United States stock markets opened in positive territory on Monday, starting a shortened holiday week with investors awaiting key appointments from the incoming presidential administration.

Five minutes into the day's trading session, the Dow Jones Industrial Average was up 0.3 per cent at 18,917.79. The broader S&P 500 and the Nasdaq both opened 0.4 per cent higher at 2,191.10 and 5,341.85 respectively.

Shares in Facebook rose 1.1 per cent following Friday's announcement that the social media network would buy back as much as US$6 billion (S$8.5 billion) of its stock in the first quarter of next year.

However, processed meat behemoth Tyson Foods saw shares tumble more than 15 per cent after reporting lower-than-expected quarterly profits on falling sales.

The company announced Monday that Chief Executive Donnie Smith will step down and the end of the year.